Composite catalyst and method for manufacturing carbon nanostructured materials

ABSTRACT

A method of forming a carbon nanotube array on a substrate is disclosed. One embodiment of the method comprises depositing a composite catalyst layer on the substrate, oxidizing the composite catalyst layer, reducing the oxidized composite catalyst layer, and growing the array on the composite catalyst layer. The composite catalyst layer may comprise a group VIII element and a non-catalytic element deposited onto the substrate from an alloy. In another embodiment, the composite catalyst layer comprises alternating layers of iron and a lanthanide, preferably gadolinium or lanthanum. The composite catalyst layer may be reused to grow multiple carbon nanotube arrays without additional processing of the substrate. The method may comprise bulk synthesis by forming carbon nanotubes on a plurality of particulate substrates having a composite catalyst layer comprising the group VIII element and the non-catalytic element. In another embodiment, the composite catalyst layer is deposited on both sides of the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/862,123 titled “Catalyst and Method for Manufacturing CarbonNanostructured Materials,” filed Oct. 19, 2006.

BACKGROUND OF THE INVENTION

Carbon nanotubes are used for a variety of applications such as insensors, reinforcement in composite materials, and the like. Althoughthere are many different ways to form carbon nanotubes, there are twodistinct types of carbon nanotubes, individual nanotubes formed by bulksynthesis and arrays of nanotubes formed by surface or orientedsynthesis. The individual nanotubes are much like spaghetti where eachnanotube is grown with random orientation. Arrays of aligned nanotubesmay include literally billions of nanotubes side-by-side, formed on asubstrate.

It has always been a goal to form longer and longer nanotubes. If longerarrays of nanotubes are formed, one can spin nanotubes into fibers thatmay be stronger and lighter than any existing fibers and that areelectrically conductive.

The short length of carbon nanotubes has been a roadblock to many oftheir applications. Growth of carbon nanotubes with controlledmorphology is an intensively investigated area. The ability to growcarbon nanotube arrays having a homogeneous and uniform structure over alarge surface area greater than one square centimeter would enablecarbon nanotube arrays to be used in many different structural andsensing applications.

Carbon nanotubes have been traditionally formed by chemical vapordeposition of carbon on a catalytic substrate. One effective catalyticsubstrate is iron. Nickel and cobalt have also been used successfully.

SUMMARY OF THE INVENTION

The present invention is premised on the realization that carbonnanotube arrays with carbon nanotubes having lengths greater than 1millimeter up to and exceeding 2 centimeters can be obtained by vapordeposition of carbon onto a catalyst coated substrate. The compositecatalyst on the substrate is a layered thin film structure comprising acombination of a known nanotube catalyst such as iron, nickel, cobalt orother group VIII elements, in combination with an element that is not aneffective catalyst by itself for carbon nanotube formation. Inparticular, the non-catalytic element is preferably a lanthanide groupmetal, such as, but not limited to, gadolinium (Gd), lanthanum (La), oreuropium (Eu). In one preferred embodiment, a composite catalyst layeris at least partially oxidized by thermal treatment in air. The oxidizedcomposite catalyst layer is then reduced to the elemental form prior tointroducing reactant gases to grow a carbon nanotube array.

In one embodiment the remaining composite catalyst layer left on thesubstrate after removing the grown CNT array is reused to grow multiplearrays without additional processing of the substrate.

In another embodiment a particulate substrate is coated by the compositecatalyst layer for bulk synthesis of carbon nanotubes.

The objects and advantages of the present invention will be furtherappreciated in light of the following detailed description and drawingsin which:

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a process flow diagram of an embodiment of the method of theinvention;

FIG. 2 is a cross-sectional view of an embodiment of a substrate with acomposite catalyst layer having a plurality of carbon nanotubes formedthereon;

FIG. 3 is a cross-sectional view of another embodiment of the substratehaving the composite catalyst layer deposited from an alloy comprising agroup VIII element and a non-catalytic element;

FIG. 4A is a cross-sectional view of another embodiment of the substratewherein the composite catalyst layer includes alternating layers of thegroup VIII element and the non-catalytic element;

FIG. 4B is a cross-sectional view of another embodiment of the substratewherein the composite catalyst layer includes four alternating layers ofthe group VIII element and the non-catalytic element;

FIG. 4C is a cross-sectional view of another embodiment of the substratewherein the composite catalyst layer includes three alternating layersof the group VIII element and the non-catalytic element;

FIG. 5A is a cross-sectional view of another embodiment of the substratehaving a discontinuous composite catalyst layer patterned on thesubstrate;

FIG. 5B is a cross-sectional view of another embodiment of the substratewherein a patterned composite catalyst layer includes alternating layersof the group VIII element and the non-catalytic element;

FIG. 5C is a cross-sectional view of another embodiment of the substratewherein a patterned catalyst layer includes four alternating layers ofthe group VIII element and the non-catalytic element;

FIG. 6A is a cross-sectional view of another embodiment with aparticulate substrate with the composite catalyst layer deposited in twoalternating layers of the group VIII element and the non-catalyticelement;

FIG. 6B is a cross-sectional view of another embodiment of theparticulate substrate having the catalytic substrate deposited in fouralternating layers of the group VIII element and the non-catalyticelement; and

FIG. 6C is a cross-sectional view of another embodiment of theparticulate substrate with the catalytic substrate deposited as an alloyof the group VIII element and the non-catalytic element.

DETAILED DESCRIPTION

Carbon nanotubes may be grown by a variety of techniques, such asoriented synthesis and bulk synthesis. In oriented synthesis, carbonnanotubes are aligned and grown in the form of an array on a substrate.The array contains many carbon nanotubes grown in one direction. In bulksynthesis, carbon nanotubes are randomly grown on many individualsubstrates, such as particulate substrates. There are a variety ofcarbon nanotube morphologies. Carbon nanotubes are usually categorizedaccording to the number of walls that the carbon nanotube has. Forexample, there are multi-walled carbon nanotubes (MWCNT), double-walledcarbon nanotubes (DWCNT), and single-walled carbon nanotubes (SWCNT). Asused herein, carbon nanotubes refers generally to any of thesemorphologies, unless otherwise stated.

With reference to FIGS. 1 and 2, in one embodiment of the invention, acarbon nanotube array 10 is formed on a substrate 20 that is compatiblewith a vapor deposition process. Initially a composite catalyst layer 30is deposited on the substrate 20 which includes a silicon dioxide layer22 and an alumina layer 24, as shown in FIG. 2. There are a variety ofvapor deposition processes to deposit and treat the various layers ofsubstrate 20. By way of example and not limitation, electron beamdeposition, thermal evaporation, spin coating, electrochemicaldeposition, electroless deposition, plasma spray deposition, magnetronsputtering, pulsed laser deposition (PLD), and chemical vapor deposition(CVD), among others. While reference may be made specifically to CVD,this term includes known modifications to CVD including, for example,plasma enhanced CVD, microwave CVD, and laser enhanced CVD. In addition,other vapor deposition processes may be utilized to grow carbonnanotubes according to the aspects of the present invention.

The substrate 20 is a single crystal silicon wafer because its use inchemical vapor deposition is very well documented. However, any inertsubstrate can be used, such as ceramics, quartz, polycrystallinesilicon, sapphire, alumina, and the like. When the substrate 20 issilicon, it is treated to form the layer of silicon dioxide 22 on itsplanar surface. A thin film of aluminum is then deposited by, forexample, electron beam deposition onto the silicon dioxide layer 22. Thethickness of the aluminum layer is not critical. Generally, it will befrom about 10 nm to about 20 nm, with 15 nm preferred.

The aluminum is oxidized by plasma oxidation to form the aluminum oxidelayer 24, also referred to as alumina. The alumina layer 24 provides aporous surface. This, in effect, creates microscopic cavities throughoutthe surface of the substrate. These cavities accommodate the compositecatalyst layer 30, forming a staging area for nucleation and growth ofthe nanotube.

The aluminum oxide layer 24 can also be formed by other thin filmdeposition methods such as direct magnetron sputtering of aluminumoxide, or direct chemical vapor deposition of aluminum oxide. The methodof forming the layer of aluminum oxide is not critical for the presentinvention. Other inert microporous substances can also be used as thebase accommodating the catalyst for the carbon nanotube formation.

The composite catalyst layer 30 is then deposited onto the substrate 20with the silicon dioxide layer 22 and the aluminum oxide layer 24deposited thereon. Any typical carbon nanotube catalyst can be used.Generally, these will be a group VIII element, including iron (Fe),cobalt (Co), nickel (Ni), ruthenium (Ru), rhodium (Rh), palladium (Pd),osmium (Os), iridium (Ir), and platinum (Pt), or combinations of these.In one embodiment, iron is a preferred catalyst due to its lower meltingpoint and its low cost compared to other group VIII elements.

In addition to the group VIII element, the composite catalyst layer 30includes a non-catalytic metal, preferably a lanthanide, for examplelanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd),promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium(Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),ytterbium (Yb), and lutetium (Lu). Other inert metals such as gold canalso be used. The weight percent (wt. %) ratio of group VIII tolanthanide element as the composite catalyst substrate can vary from5/95 to 95/5. The weight percent ratios that are more effective inproducing carbon nanotubes include 20/80, preferably 50/50, and morepreferably 95/5.

The composite catalyst layer 30 can be deposited by any well-knownmethod, such as e-beam deposition, magnetron sputtering, or chemicalvapor deposition, in one of at least two manners. In order to achievethe desired catalyst ratio, an alloy of the group VIII and thelanthanide element (or non-catalytic metal) can be used to deposit thecomposite catalyst layer 30. The composite catalyst layer 30 may also beformed by simultaneously sputtering from multiple sputtering targets.The elements sputtered from the targets may then combine on thesubstrate 20.

As shown in FIG. 4A, the composite catalyst layer 30 may also be formedby depositing alternating layers of the group VIII element and thenon-catalytic element. The first layer 32 may comprise iron with thesecond layer 34 comprising gadolinium, or the reverse construction isalso possible. The amount or weight percent ratio of the two metals,i.e., iron and gadolinium is controlled by the thickness of the layer.

As shown in FIG. 4B, multiple alternating layers can be deposited ontoone another. FIG. 4B is an illustration of four alternating layers.Again, the thickness and number of layers determine the amount of groupVIII and non-catalytic element deposited. The composite catalyst layer30 may also comprise an odd number of layers, for example the threelayers 32, 34, 36 as depicted in FIG. 4C. Thus, the amount of the groupVIII element relative to the amount of the non-catalytic element may bemodified by changing the number of layers of either the group VIIIelement or the non-catalytic element. In addition, the individualthicknesses of the layers may be changed to bring about a particularmass ratio of the group VIII element to non-catalytic element in thecatalytic layer 30.

The applied thickness of the composite catalyst layer 30 should be fromabout 0.5 to about 5 nanometers (nm), with between about 1 and about 2nm being preferred. Thus, the thickness of layers 32 and 34 should eachmeasure about 1 nm. One preferred structure includes one layer of ironhaving a thickness of about 1 nm and one layer of gadolinium having athickness of 1 nm. In this case, the weight percent ratio of iron togadolinium is about 50/50 since the iron and gadolinium densities areapproximately the same. With reference to FIG. 4B, another preferredstructure includes four alternating layers of iron and gadolinium, eachabout 0.5 nm thick. For example, a first layer 32 may comprise iron, asecond layer 34 may comprise gadolinium, a third layer 36 may compriseiron, and a fourth layer 38 may comprise gadolinium such that theindividual thicknesses total about 2 nm. More layers are possible,however, controlling the thickness uniformity becomes increasingly moredifficult for layers with thicknesses of 0.5 nm and less. Even thoughalternating layers are described, the layers may be deposited indifferent orders.

A third catalytic component can be added to the composite catalyst layer30. The third component can be an additive catalyst typically used incarbon nanotube growth. These include, for example, yttrium (Yt) andtantalum (Ta), as well as scandium (Sc), titanium (Ti), vanadium (V),chromium (Cr), manganese (Mn), zirconium (Zr), niobium (Nb), molybdenum(Mo), hafnium (Hf), tungsten (W), and rhenium (Rh). These can be addedto the composite catalyst layer 30 in the same manner as the group VIIIand the non-catalytic elements.

As shown in FIGS. 5A, 5B, and 5C, the composite catalyst layer 30 may bedeposited as a discontinuous layer, i.e., in a pattern. The pattern mayhave a plurality of coated areas 40 of the group VIII element and thenon-catalytic element deposited from the alloy, as depicted in FIG. 5A,again with a total thickness preferably of about 2 nm. The coated areas40 may be separated by an uncoated area 50. Preferably, the areas ofcatalyst deposition are separated from each other by a spacing of about0.01 to about 3 millimeters. One preferred pattern consists of 1millimeter diameter circles of catalyst separated by about 1 millimeterof uncoated substrate, although other patterns are possible. Inaddition, the pattern may be deposited as a plurality of alternatinglayers 40, 42 of the group VIII catalyst and the non-catalytic element,as shown in FIG. 5B. Therefore, in one embodiment, the coated areas 40have a first layer 42, and a second layer 44. The total height of thecatalytic layer 30 may be, for example, about 2 nm. Similarly, asillustrated in FIG. 5C, the catalytic layer 30 may include fouralternating group VIII/non-catalytic layers 42, 44, 46, 48. The totalheight of the coated area 40 may be between approximately 0.5 nm andapproximately 5 nm with 2 nm being preferred.

Once the composite catalyst layer 30 is deposited, it is desirable tobreak up the composite catalyst layer 30 into small particles(nanoclusters). This can be accomplished by heating the compositecatalyst layer 30 in an air environment at a temperature of betweenapproximately 300 and 900° C., preferably about 300° C. to about 500°C., most preferably about 400° C. for about 5 hours, although thetemperature may vary with the composition of the group VIII element.This treatment will at least partially oxidize the group VIII elementand cause it to form small (about 4 nm to about 40 nm) nanoclusters ofthe group VIII oxide in a layer.

The size of the small nanoclusters of the composite catalyst layer 30may be influenced by the melting temperature of the composite catalystlayer 30. As the melting temperature of the composite catalyst layer 30decreases, the nanoclusters may decrease in size. The smallernanoclusters produce smaller diameter carbon nanotubes and promote DWCNTgrowth. The melting point may be reduced by depositing different metalswhich have a low melting temperature or alloys forming low temperatureeutectics. For example, an iron-lanthanum alloy will have a lowermelting point than pure iron or pure lanthanum. Thus, a catalystdeposited from such an alloy or deposited as alternating layers willhave a lower melting point than pure iron. The oxidized compositecatalyst layer is later reduced forming the metal catalyst nanoclustersprior to growing the carbon nanotube array 10. The oxidized compositecatalyst layer is preferably reduced by heating the composite catalystlayer 30 to about 700° C. in hydrogen.

The method of oxidizing and reducing a catalyst layer prior to growingcarbon nanotubes produces surprising results even without the lanthanidepresent. When the composite catalyst layer 30 comprises the group VIIIelement and the non-catalytic element even better results are achieved.

The carbon nanotube array 10 is grown by thermal chemical vapordeposition utilizing a gas mixture of hydrogen, ethylene, water, andargon. An EasyTube Furnace from First Nano, Inc., can be used, althoughother known methods of depositing carbon nanotubes can be employed. Inone preferred embodiment, the chemical vapor deposition is initiatedwith an argon flow at about 400° C. followed by hydrogen flow at about700° C. to convert the group VIII oxide back to elemental group VIII.

The actual growth of the carbon nanotubes start when a mixture ofhydrogen, ethylene, water, and argon is applied at a temperature of 700°C. to 800° C., preferably about 750° C. Besides ethylene, other carbonprecursors, such as, methane, acetylene, methanol, ethanol and carbonmonoxide may be used. The water may be supplied by flowing argon througha water bubbler operating at room temperature. The gas flow isintroduced into the reactor for about 10 hours or until carbon nanotubegrowth stops.

The mixture of the gases flowing into the reactor may vary. For example,the volumetric ratio of argon flowing through a water bubbler to themain argon flow going through the reactor may be between 0.5 and 3, thevolumetric ratio of ethylene to argon may be between 0.5 and 1, thevolumetric ratio of ethylene to hydrogen may be between 0.5 and 3, andthe volumetric ratio of the hydrogen to argon may be between 0.5 to 1.For example, in one preferred embodiment, ethylene is introduced at 200sccm with argon flowing at 300 sccm, hydrogen flowing at 200 sccm, andargon flowing through the room temperature bubbler at 150 sccm.

The flux of carbon to the catalyst particle is a significant variablethat influences the degree to which carbon can be delivered to thesubstrate, and form carbon nanotubes. The water in the reaction gas isdesigned to drive off unwanted amorphous carbon that can block thecatalyst function. Therefore, about 150 sccm of argon carrier gas ispassed through a bubbler to carry a sufficient amount of water to removethe amorphous carbon but not the graphitic carbon that forms the carbonnanotubes. The carbon vapor deposition is continued as long as thecarbon nanotubes continue to grow. Before the growth stops, additionalcatalysts can be added to promote further growth. Specifically, feroceneor iron pentacarbonyl can be added to the reaction mixture, which willthen deposit iron onto the surface of the nanotubes, which will act as acatalyst to further increase growth.

The carbon nanotubes grown in accordance with another embodiment of themethod include MWCNTs when the composite catalyst layer 30, as shown inFIG. 3, is deposited from an alloy of the group VIII element and thenon-catalytic element, for example from an alloy of iron and gadolinium.Thus, the iron and gadolinium are deposited substantiallysimultaneously. Generally the MWCNTs exhibit a diameter of about 20nanometers. In another embodiment with the composite catalyst layer 30deposited, as shown in FIG. 4A with one layer of iron of about 1 nm withone layer of lanthanum about 1 nm thick on top, the MWCNTs havediameters of about 15 nm. MWCNTs and some DWCNTs grow when the compositecatalyst layer 30 is deposited in alternating layers of iron andgadolinium, as illustrated in FIGS. 4A and 4B. While the alternatinglayers, previously described, are more cost effective than the alloy,they also generally grow carbon nanotubes having lengths greater thanthe carbon nanotubes grown on the composite catalyst layer 30 depositedfrom the alloy.

SWCNTs may grow by controlling the composition of the composite catalystlayer 30, the structure of the composite catalyst layer 30, annealing ofthe composite catalyst layer 30, the nature of the carbon precursor, andthe growth conditions in the reactor. The composition of the compositecatalyst layer 30 may affect the number of walls of the carbon nanotube.As the atomic radius of the group VIII and the non-catalytic elementsdecrease, the size of the catalyst nanoparticles produced duringannealing of the composite catalyst layer 30 decreases. The smallersized catalyst particles (nanoclusters) produce smaller diameter carbonnanotubes. In addition to the atomic radius of the catalyst, the layeredstructure of the catalyst influences the size of the carbon nanotubes.An annealing temperature that produces smaller particles during thethermal treatment in air may permit SWCNTs and DWCNTs to grow,preferably the catalyst particles produced should be below 5 nm in size.To produce small catalyst particles the temperature during a shortthermal treatment of 10 minutes should preferably be above 500° C. andclose to 900° C.

The carbon precursors, like ethylene and acetylene are reactive atelevated temperatures and have higher decomposition rates and are likelyto grow MWCNT because they generate higher carbon flux. To grow SWCNTand DWCNT, the amount of reactive carbon is reduced by selecting anappropriate precursor, such as methane. Methane is more thermally stablethan ethylene and acetylene and thus requires less management, such asdilution for controlled carbon partial pressure and carbonflux.

The growth conditions in the reactor, particularly the flow rates of thehydrogen gas, argon gas, carbon precursor, and the temperature, affectthe morphology of the carbon nanotube growth. Hydrogen is introduced todilute the precursor and to control the decomposition of the hydrocarbonprecursor. Thus controlling hydrogen flow can prevent unnecessary excessof carbon within a carbon nanotube growth zone, particularly amorphouscarbon. The greater the flow rate of hydrogen gas the higher theprobability of SWCNT growth. Hydrogen and argon act as diluting gasespreventing amorphous carbon formation. Argon flow dilutes the carbonprecursor and decreases the flux of carbon atoms towards the growthzone. As the flux of carbon atoms decreases the probability of SWCNTgrowth increases because the hydrogen may prevent the formation ofamorphous carbon. The flow of the carbon precursor should likewise bekept low to prevent the formation of amorphous carbon. Low carbonprecursor flow rate is more likely to produce SWCNT growth.

The growth temperature influences the morphology of the carbon nanotube.In general, elevated temperatures increase the surface mobility of thecarbon atoms. Thus higher temperatures, preferably between about 800° C.and 1000° C., increase the probability of growing carbon nanotubeshaving a minimum number of walls. However, high temperatures alsoincrease the decomposition rate of the precursor. The higherdecomposition rate may therefore be balanced with an increase in theflow of argon and/or hydrogen gas to control the carbon flux and helpprevent formation of amorphous carbon.

One preferred reactor uses a three-zone furnace. The growth is conductedin a middle zone. In the first zone the reactant gases are preheated tofor example 450° C. In the third section, the exhaust gases aremaintained at a higher temperature, such as 400° C. Thus, the three-zonefurnace helps control the temperature in the middle zone.

In one embodiment, improved production of the carbon nanotubes isachieved by using the composite catalyst layer 30 to regrow multiplearrays 10 on a same substrate without additional processing of thesubstrate 20. In other words, by removing the carbon nanotubes from thecomposite catalyst layer 30, additional carbon nanotubes may be grown onthe same composite catalyst layer 30. The composite catalyst layer 30 isnot reprocessed between successive periods of growing carbon nanotubes.By way of example, removing the grown carbon nanotubes from thecomposite catalyst layer 30 may only require a slight physical pressure,particularly when the carbon nanotubes are in the reactor at elevatedtemperatures. Growth of additional carbon nanotubes on the compositecatalyst layer 30 follows removal of the preceding carbon nanotubes.Thus, a single substrate 20 having a composite catalyst layer 30 mayyield multiple arrays 10 of carbon nanotubes.

The composite catalyst layer 30 can also be deposited on two opposingsides of the substrate 20 for increased productivity. The substrate 20is oriented, for example on one edge, such that each composite catalystlayer 30 on both sides of the substrate 20 is exposed to the reactantgases. The carbon nanotubes grow according to the previously describedprocedure; however, the carbon nanotubes grow from each side of thesubstrate 20 simultaneously. In addition, or alternatively, increasedproductivity may be obtained by depositing the composite catalyst layer30 over very large substrates, such as on substrates exceeding tens ofcentimeters along each dimension. For example, the composite catalystlayer 30 may be deposited with magnetron sputtering onto these largesubstrates. The composite catalyst layer 30 may also be deposited withCVD technique on these large substrates.

Bulk synthesis of carbon nanotubes are grown on a plurality ofparticulate substrates 60. FIGS. 6A, 6B, and 6C illustrate crosssections of spherical particulate substrates 60. However, the shape ofthe particulate substrate 60 is not critical. The particulate substrate60 is generally a nonreactive, refractory particle having hightemperature stability, for example, magnesium oxide (MgO), alumina(Al₂O₃), silica (SiO₂), or other oxides.

The composite catalyst layer 30 is preferably deposited onto theparticulate substrate 60 in alternating layers, discussed above. Theindividual layers comprise the group VIII element or the non-catalyticelement. For example, as shown in FIG. 6A, the composite catalyst layer30 coats the particulate substrate 60 such that a first layer 62 coatsthe particulate substrate 60 and the second or outer layer 64 coats thefirst layer 62. One preferred structure has alternating layers of ironand gadolinium. In another embodiment, the composite catalyst layer 30has four alternating layers of the group VIII element and thenon-catalytic element. For example, as depicted in FIG. 6B, the firstlayer 62 comprising iron is deposited on the particulate substrate 60with a second layer 64 comprising gadolinium is deposited on the firstlayer 62, a third layer 66 comprising iron is deposited on the secondlayer 64, and a fourth layer 68 comprising gadolinium is deposited onthe third layer 66.

The catalyst layer 60 may be deposited from an alloy to create thecatalytic layer 30 on the particulate substrate 60. For example, asillustrated in FIG. 6C, the particulate substrate 60 may be coated froman alloy comprising iron and gadolinium.

The composite catalyst layer 30 can be deposited onto the particulatesubstrate 60 and the substrate 20 by any well-known method, such as aplasma deposition system, e.g., an radio-frequency plasma or a microwaveplasma CVD. With the plasma deposition, the group VIII element and thenon-catalytic element can be bonded to the particulate substrate 60 orthe substrate 20. For example, the plasma CVD produces the compositecatalyst layer 30 having iron onto the particulate substrates 60 whenferrocene vapor, Fe(C₅H₅)₂ is introduced into the plasma. Similarly, inanother example, iron deposits when an iron precursor, such as ironpentacarbonyl, Fe(CO)₅ is introduced into the system. To deposit acomposite catalyst layer 30 having gadolinium, a gadolinium precursor isintroduced, such as gadolinium chloride GdCl₃, gadolinium propoxideGd(OC₃H₇ ^(i)), gadolinium (2,2,6,6-tetramethyl-3,5-heptanedionate),Gd(C₁₁H₁₉O₂)₃ tris(cyclopentadienyl), gadolinium (C₅H₅)₃ Gdtris(tetramethylcyclopentadienyl), and gadolinium [(CH₃)₄C₂H]₃ Gd. Anyof the precursors having low vapor pressure may be introduced into theplasma system with a bubbler, either from solid state or from solution.Similarly, other group VIII elements can be introduced into the plasmasystem in order to deposit the composite catalyst layer 30 onto theparticulate substrate 60 or the substrate 20.

Other methods such as electro-less deposition, electrochemicaldeposition, calcination on the particulate substrate 60 in the presenceof one or more salts comprising the catalyst layer composition, CVD,e-beam deposition, magnetron sputtering, thermal evaporation, sol-gelsynthesis, ball milling the particulate substrates 60 within a mixtureof one or more salts or oxides comprising the group VIII element or thenon-catalytic element or a combination of oxides and salts, or any thinfilm technique may be used to deposit the composite catalyst layer 30.Next, bulk synthesis of carbon nanotubes on the particulate substrates60 proceeds according to the growing step as outlined above with respectto the carbon nanotube array 10.

The invention can also be practiced using a floating catalyst. In thisembodiment the catalyst is introduced as a gas using, for example,vaporized ferrocene or cobaltocene and gadolinium chloride gas. Thecatalyst gases are introduced with the reactant gases, such as ethylene,as previously described. Generally the catalyst gas will comprise about1 to about 3 volume % of the total gas flow into the reactor. Thecatalyst will be about 95 to about 5 wt. % of the group VIII element andabout 5 to about 95 wt. % of the lanthanide element, as with the layeredcomposite catalyst 30.

In order to facilitate a more complete understanding of the method ofthe invention, the following non-limiting examples are provided.

EXAMPLE 1

A 15 nm Al film was deposited by e-beam deposition onto an oxidizedsingle crystal silicon wafer. The SiO₂ layer had a thickness ofapproximately 500 nm. The Al film was converted into aluminum oxide byexposing it for about 10 minutes in a radio frequency plasma environmentcontaining about 20 vol. % O₂ and about 80 vol. % Ar. The radiofrequency plasma power was 300 W and the oxidation was performed atpressure of 60 Torr.

A composite catalyst layer having a thickness of about 2 nm wasdeposited by e-beam deposition on top of the aluminum oxide. Thecomposite catalyst layer was formed from an alloy of about 80 wt. % ironand about 20 wt. % gadolinium.

The substrate and the composite catalyst film were then thermallyannealed for 5 hours at 400° C. in air. Following annealing, thesubstrate was loaded into a CVD reactor to grow a carbon nanotube array.The reactor was purged with about 1000 sccm argon for about 10 minutesat room temperature before the temperature was increased. The substrateand the composite catalyst layer where heated to about 400° C. and heldat that temperature for about 20 minutes to permit the argon flow topreheat. To reduce the oxidized composite catalyst layer, thetemperature was increased up to 700° C. and a flow of about 200 sccmhydrogen was introduced into the reactor for about 15 minutes. Thetemperature of the CVD reactor was increased to about 750° C. Thesubstrate and reduced composite catalyst layer were held at thattemperature for about 10 hours while several gases were introduced intothe reactor to grow the carbon nanotube array.

The following gases and their flow rates were adjusted and introducedinto the reactor to grow the carbon nanotube array: ethylene at 200sccm, Ar at 300 sccm, and water vapor carried by Ar flowing at 150 sccmpassing through a room temperature bubbler, and hydrogen at 200 sccm.After ten hours, the reactor was cooled to room temperature in a flow of500 sccm Ar. This method produced a CNT array having carbon nanotubes ofapproximately 7 mm in length.

EXAMPLE 2

A composite catalyst layer was deposited onto a silicon substrateprepared as described in Example 1. The composite catalyst layer had athickness of about 2 nm and was formed from an alloy having an iron togadolinium weight percent ratio of about 50/50.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array having carbon nanotubes ofapproximately 5 mm in length.

EXAMPLE 3

A composite catalyst layer was deposited onto a silicon substrateprepared as described in Example 1. The composite catalyst layer had athickness of about 2 nm and was formed from an alloy having an iron togadolinium weight percent ratio of about 20/80.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedure described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time

This method produced a CNT array having carbon nanotubes ofapproximately 7.5 mm in length.

EXAMPLE 4

A composite catalyst layer was deposited onto a silicon substrateprepared as described in Example 1. The composite catalyst layer had athickness of about 2 nm and was formed from an alloy having an iron togadolinium weight percent ratio of about 95/5.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array having carbon nanotubes ofapproximately 7 mm in length.

EXAMPLE 5

A composite catalyst layer, having two alternating layers, was depositedon a silicon substrate prepared as described in Example 1. The compositecatalyst layer was formed with a gadolinium layer having a thickness ofabout 1 nm on top of an iron layer having a thickness of about 1 nm.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array having carbon nanotubes ofapproximately 8 mm in length.

EXAMPLE 6

A composite catalyst layer having two alternating layers was depositedon the silicon substrate prepared as described in Example 1. Thecomposite catalyst layer was formed by depositing an iron layer having athickness of about 1 nm on top of a gadolinium layer having a thicknessof about 1 nm.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array having carbon nanotubes ofapproximately 6 mm in length.

EXAMPLE 7

A composite catalyst layer, having four alternating layers, wasdeposited on the silicon substrate prepared as described in Example 1.The composite catalyst layer was formed from four alternating layerswith each layer having a thickness of about 0.5 nm. The layers weredeposited as follows: iron, gadolinium, iron, and gadolinium, withgadolinium being the topmost layer.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array having carbon nanotubes ofapproximately 11.5 mm in length.

This procedure was independently reproduced with a three zone CVDreactor and 18 mm growth was achieved.

EXAMPLE 8

A composite catalyst layer, having four alternating layers, wasdeposited on the silicon substrate prepared as described in Example 1.Each layer had a thickness of about 0.5 nm. The layers were deposited asfollows: gadolinium, iron, gadolinium, and iron, with iron being thetopmost layer.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array having carbon nanotubes ofapproximately 9 mm in length.

EXAMPLE 9

A composite catalyst layer having a thickness of approximately 2 nm wasdeposited from an alloy having a weight percent ratio of iron togadolinium of about 80/20 by e-beam deposition through a shadow maskwith holes of 1 mm in diameter and spacing between the holes of 1 mm.This procedure created a patterned composite catalyst substrate.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions, except the CNT array was grown over 6 hours rather than 10hours.

This method produced a CNT array of uniform posts having carbonnanotubes of approximately 8 mm in length.

EXAMPLE 10

A composite catalyst layer having a thickness of approximately 2 nm wasdeposited from an alloy having an iron to gadolinium weight percentratio of about 50/50 by e-beam deposition through a shadow mask withholes of 1 mm in diameter and spacing between the holes of 1 mm. Thisprocedure created a patterned composite catalyst substrate.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array of uniform posts having carbonnanotubes of approximately 5 mm in length.

EXAMPLE 11

A composite catalyst layer having a thickness of approximately 2 nm wasdeposited from an alloy having an iron to gadolinium weight percentratio of about 20/80 by e-beam deposition through a shadow mask withholes of 1 mm in diameter and spacing between the holes of 1 mm. Thisprocedure created a patterned composite catalyst substrate.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array of uniform posts having carbonnanotubes of approximately 6 mm in length.

EXAMPLE 12

A composite catalyst layer having a thickness of approximately 2 nm wasdeposited from an alloy having an iron to gadolinium weight percentratio of about 95/5 by e-beam deposition through a shadow mask withholes of 1 mm in diameter and spacing between the holes of 1 mm. Thisprocedure created a patterned composite catalyst substrate.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array of uniform posts having carbonnanotubes of approximately 2.5 mm in length.

EXAMPLE 13

A composite catalyst layer was deposited through a shadow mask withholes of 1 mm in diameter and spacing between the holes of 1 mm. Thecomposite catalyst layer was comprised of four alternating layers witheach layer having a thickness of about 0.5 nm. The layers were depositedas follows: iron, gadolinium, iron, and gadolinium with gadolinium beingthe topmost layer.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array of uniform posts having carbonnanotubes of approximately 8 mm in length.

EXAMPLE 14

A composite catalyst layer having a thickness of approximately 2 nm wasdeposited from an alloy having an iron to gadolinium weight percentratio of about 80/20 by e-beam deposition through a shadow mask withholes of 0.1 mm in diameter and spacing between the holes of 0.1 mm.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array of uniform posts having carbonnanotubes of approximately 8 mm in length.

EXAMPLE 15

A composite catalyst layer having a thickness of approximately 2 nm wasdeposited from an alloy having an iron to gadolinium weight percentratio of about 80/20 by e-beam deposition through a shadow mask withholes of 0.01 mm in diameter and spacing between the holes of 0.01 mm.The shadow mask was comprised of polymethyl methacrylate (PMMA) whichwas manufactured directly on the surface of the substrate using e-beamlithography.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions, except that the CNT array was grown for one hour rather than10 hours.

This method produced a CNT array of uniform posts having carbonnanotubes of approximately 0.5 mm in length.

EXAMPLE 16

A composite catalyst layer was deposited with lanthanum rather thangadolinium. The composite catalyst layer was formed with a layer oflanthanum on top of a layer of iron. Each layer had a thickness ofapproximately 1 nm.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array having carbon nanotubes ofapproximately 9 mm in length.

EXAMPLE 17

A composite catalyst layer was deposited with lanthanum rather thangadolinium. The composite catalyst layer was formed with a layer of ironon top of a layer of lanthanum. Each layer had a thickness ofapproximately 1 nm.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array having carbon nanotubes ofapproximately 10 mm in length.

EXAMPLE 18

A composite catalyst layer was deposited with gold rather thangadolinium. The composite catalyst layer formed with a layer of gold ontop of a layer of iron. Each layer had a thickness of approximately 1nm.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array having carbon nanotubes ofapproximately 1 mm in length.

EXAMPLE 19

A composite catalyst layer was deposited with gold (Au) rather thangadolinium. The composite catalyst layer was therefore formed of a layerof gold on top of a layer of iron with each layer having a thickness ofapproximately 1 nm. The substrate was annealed for 10 minutes at 850° C.in air and then loaded into the CVD reactor. The nanotubes were grownunder conditions similar to the Example 1 conditions and time.

This method produced a CNT array having carbon nanotubes ofapproximately 0.3 mm in length.

EXAMPLE 20

The composite catalyst layer was deposited from an alloy ofapproximately 20 wt. % iron and approximately 80 wt. % gadolinium. Thecomposite catalyst layer was about 2 nm thick. The substrate and thecomposite catalyst layer were annealed and reduced according to theprocedures described in Example 1. In addition, the nanotubes were grownunder conditions similar to the Example 1 conditions and time.

This method produced a CNT array having carbon nanotubes ofapproximately 7.5 mm in length.

This CNT array was removed from the substrate and the substrate wasplaced directly into the CVD reactor without any additional processing.The substrate and the composite catalyst layer were again exposed to thegrowth conditions described in Example 1. This method produced a CNTarray having carbon nanotubes of approximately 1 mm in length.

EXAMPLE 21

A composite catalyst layer having four alternating layers was depositedon the substrate prepared as described in Example 1. Each alternatinglayer had a thickness of about 0.5 nm. The layers were deposited asfollows: iron, gadolinium, iron, and gadolinium, with gadolinium beingthe topmost layer.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array having carbon nanotubes ofapproximately 11 mm in length.

This CNT array was removed from the substrate and the substrate wasplaced directly into the CVD reactor without any additional processing.The substrate and the composite catalyst layer were again exposed to thegrowth conditions described in Example 1. This method produced a CNTarray having carbon nanotubes of approximately 8 mm in length. Thisprocedure was independently reproduced in a three zone CVD reactor, aspreviously described.

EXAMPLE 22

A composite catalyst layer was deposited with lanthanum rather thangadolinium. The composite catalyst layer comprised a layer of lanthanumon top of a layer of iron. Each layer had a thickness of approximately 1nm.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array having carbon nanotubes ofapproximately 9 mm in length.

This CNT array was removed from the substrate and the used substrate wasplaced directly into the CVD reactor without any additional processing.The substrate and the composite catalyst layer were again exposed to thegrowth conditions described in Example 1. This method produced a CNTarray having carbon nanotubes of approximately 1.5 mm in length.

EXAMPLE 23

A composite catalyst layer was deposited with lanthanum rather thangadolinium. The composite catalyst layer comprised a layer of iron ontop of a layer of lanthanum. Each layer had a thickness of approximately1 nm.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions and time.

This method produced a CNT array having carbon nanotubes ofapproximately 10 mm in length.

This CNT array was removed from the substrate and the substrate wasplaced directly into the CVD reactor without any additional processing.The substrate and the composite catalyst layer were again exposed to thegrowth conditions described in Example 1. This method produced a CNTarray having carbon nanotubes of approximately 2 mm in length.

EXAMPLE 24

A composite catalyst layer, having three alternating layers, wasdeposited on the silicon substrate prepared as described in Example 1.Each of the layers was about 0.5 nm thick. The composite catalyst layerwas formed by depositing iron on the substrate, a gadolinium layer, andanother layer of iron on top.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions; however, the array was permitted to grow over about 5 hoursrather than 10 hours.

This method produced a CNT array having carbon nanotubes ofapproximately 3 mm in length.

EXAMPLE 25

A composite catalyst layer, having three alternating layers, wasdeposited on the silicon substrate prepared as described in Example 1.Each of the layers was about 0.5 nm thick. The composite catalyst layerwas formed by depositing gadolinium on the substrate, an iron layer, andanother layer of gadolinium on top.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions; however, the array was permitted to grow over about 5 hoursrather than 10 hours.

This method produced a CNT array having carbon nanotubes ofapproximately 5 mm in length.

EXAMPLE 26

A composite catalyst layer, having three alternating layers, wasdeposited on the silicon substrate prepared as described in Example 1.Each of the layers was about 0.5 nm thick. The composite catalyst layerwas formed by depositing iron on the substrate, a lanthanum layer, andanother layer of iron on top.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions; however, the array was permitted to grow over about 5 hoursrather than 10 hours.

This method produced a CNT array having carbon nanotubes ofapproximately 4 mm in length.

EXAMPLE 27

A composite catalyst layer, having three alternating layers, wasdeposited on the silicon substrate prepared as described in Example 1.Each of the layers was about 0.5 nm thick. The composite catalyst layerwas formed by depositing lanthanum on the substrate, an iron layer, andanother layer of lanthanum on top.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions; however, the array was permitted to grow over about 5 hoursrather than 10 hours.

This method produced a CNT array having carbon nanotubes ofapproximately 3 mm in length.

EXAMPLE 28

A composite catalyst layer, having two alternating layers, was depositedon a silicon substrate prepared as described in Example 1. The compositecatalyst layer was formed with a europium layer having a thickness ofabout 1 nm on top of an iron layer having a thickness of about 1 nm.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions; however, the carbon nanotubes were grown for a period ofabout 5 hours rather than 10 hours.

This method produced a CNT array having carbon nanotubes ofapproximately 1 mm in length.

EXAMPLE 29

A composite catalyst layer having two alternating layers was depositedon the silicon substrate prepared as described in Example 1. Thecomposite catalyst layer was formed by depositing an iron layer having athickness of about 1 nm on top of a europium layer having a thickness ofabout 1 nm.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions; however, the carbon nanotubes were grown for a period ofabout 5 hours rather than 10 hours.

This method produced a CNT array having carbon nanotubes ofapproximately 0.1 mm in length.

EXAMPLE 30

A composite catalyst layer, having four alternating layers, wasdeposited on the silicon substrate prepared as described in Example 1.The composite catalyst layer was formed from four alternating layerswith each layer having a thickness of about 0.5 nm. The layers weredeposited as follows: iron, europium, iron, and europium, with europiumbeing the topmost layer.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions; however, the carbon nanotubes were grown for a period ofabout 5 hours rather than 10 hours.

This method produced a CNT array having carbon nanotubes ofapproximately 2 mm in length.

EXAMPLE 31

A composite catalyst layer, having four alternating layers, wasdeposited on the silicon substrate prepared as described in Example 1.Each layer had a thickness of about 0.5 nm. The layers were deposited asfollows: europium, iron, europium, and iron, with iron being the topmostlayer.

The substrate and the composite catalyst layer were annealed and reducedaccording to the procedures described in Example 1. In addition, thenanotubes were grown under conditions similar to the Example 1conditions; however, the carbon nanotubes were grown for a period ofabout 5 hours rather than 10 hours.

This method produced a CNT array having carbon nanotubes ofapproximately 1 mm in length.

As shown in these non-limiting examples, the method of the invention canbe used to grow carbon nanotubes exceeding 10 mm in length, and in oneexample approaching 12 mm in length, over a period of about 10 hours.The carbon nanotubes included MWCNTs and DWCNTs. This has been adescription of the present invention along with the preferred method ofpracticing the present invention. However, the invention itself shouldonly be defined by the appended claims.

1. A method of forming a plurality of carbon nanotubes on a substrate comprising: depositing a composite catalyst layer on said substrate, wherein said composite catalyst layer comprises a group VIII element and a non-catalytic element, said non-catalytic element comprising a metal that does not catalyze nanotube growth by itself; oxidizing said composite catalyst layer to form an oxidized composite catalyst layer; reducing said oxidized composite catalyst layer to form a reduced composite catalyst layer; and growing said carbon nanotubes on said reduced composite catalyst layer.
 2. The method of claim 1 wherein said group VIII element comprises at least one of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, or Pt or a combination thereof.
 3. The method of claim 1 wherein said non-catalytic element comprises a Lanthanide.
 4. The method of claim 1 wherein said non-catalytic element comprises Gd.
 5. The method of claim 1 wherein said non-catalytic element comprises La.
 6. The method of claim 1 wherein said non-catalytic element comprises Eu.
 7. The method of claim 1 wherein said non-catalytic element comprises Au.
 8. The method of claim 1 wherein said composite catalyst layer has a thickness greater than approximately 0.5 nm.
 9. The method of claim 1 wherein said composite catalyst layer has a thickness of between approximately 1 nm and approximately 2 nm.
 10. The method of claim 1 wherein said carbon nanotubes are formed in a chemical vapor deposition reactor.
 11. The method of claim 1 wherein during depositing said composite catalyst layer, said group VIII element and said non-catalytic element are deposited onto said substrate substantially simultaneously.
 12. The method of claim 11 wherein said composite catalyst layer comprises at least approximately 5 wt. % of said group VIII element.
 13. The method of claim 11 wherein said composite catalyst layer comprises at least approximately 50 wt. % of said group VIII element.
 14. The method of claim 11 wherein said composite catalyst layer comprises at least approximately 95 wt. % of said group VIII element.
 15. The method of claim 1 comprising depositing a plurality of alternating layers of said group VIII element and said non-catalytic element on to said substrate.
 16. The method of claim 1 wherein said composite catalyst layer is a discontinuous layer having a pattern comprising a plurality of coated areas separated by approximately 0.01 mm to approximately 3 mm of an uncoated area.
 17. The method of claim 16 wherein said coated areas are about 1 mm in diameter.
 18. The method of claim 1 wherein during oxidizing said composite catalyst layer, said composite catalyst layer is heated to an annealing temperature of between approximately 300° C. and approximately 900° C.
 19. The method of claim 1 wherein during oxidizing said composite catalyst layer, said composite catalyst layer is heated to an annealing temperature of between approximately 300° C. and approximately 500° C.
 20. The method of claim 1 wherein reducing said oxidized composite catalyst layer comprises heating said oxidized composite catalyst layer to between approximately 600° C. and approximately 800° C. in a reducing gas.
 21. The carbon nanotubes grown by the method claimed in claim
 1. 22. A method of forming a plurality of carbon nanotubes on a substrate comprising: depositing a composite catalyst layer on said substrate, wherein said composite catalyst layer has a thickness of between approximately 1 nm and approximately 2 nm and comprises a group VIII element and a non-catalytic element, said non-catalytic element comprising a metal that does not catalyze nanotube growth by itself; oxidizing said composite catalyst layer by heating said composite catalyst layer to an annealing temperature of between approximately 300° C. and approximately 900° C. to form an oxidized composite catalyst layer; reducing said oxidized composite catalyst layer by heating said oxidized composite catalyst layer to between approximately 600° C. and approximately 800° C. in a reducing gas to form a reduced composite catalyst layer; and growing said carbon nanotubes on said reduced composite catalyst layer.
 23. The method of claim 22 wherein during depositing said composite catalyst layer, said group VIII element and said non-catalytic element are deposited onto said substrate substantially simultaneously.
 24. The method of claim 22 comprising depositing a plurality of alternating layers of said group VIII element and said non-catalytic element on to said substrate.
 25. The method of claim 24 wherein a number of said alternating layers is an odd number.
 26. A method of forming carbon nanotubes with a plurality of particulate substrates comprising: depositing a composite catalyst layer on said particulate substrate, wherein said composite catalyst layer comprises a plurality of alternating layers of a group VIII element and a non-catalytic element, and wherein said group VIII element comprises at least one of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, or Pt or a combination thereof, and said non-catalytic element comprises a lanthanide; and growing said carbon nanotubes on said composite catalyst layer.
 27. A particulate substrate for bulk synthesis of a plurality of carbon nanotubes comprising: an oxide particulate; and a composite catalyst layer coating said oxide particulate, wherein said composite catalyst layer comprises a plurality of alternating layers of a group VIII element and a non-catalytic element.
 28. The particulate substrate of claim 27 wherein said group VIII element comprises at least one of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, or Pt or a combination thereof.
 29. The particulate substrate of claim 27 wherein said non-catalytic element comprises a Lanthanide.
 30. The particulate substrate of claim 27 wherein said non-catalytic element comprises gadolinium.
 31. The particulate substrate of claim 27 wherein said non-catalytic element comprises lanthanum.
 32. A method of forming carbon nanotubes comprising growing said carbon nanotubes on a composite catalyst layer comprising a group VIII metal in its elemental form and a non-catalytic metal in its elemental form.
 33. The method of claim 32 wherein said non-catalytic metal is a Lanthanide.
 34. A method of forming a plurality of carbon nanotubes on a substrate comprising: processing a catalyst layer on said substrate, wherein said catalyst layer comprises a group VIII element; oxidizing said catalyst layer to form an oxidized catalyst layer; reducing said oxidized catalyst layer to form a reduced catalyst layer; and growing said carbon nanotubes on said reduced catalyst layer with chemical vapor deposition.
 35. The method of claim 34 wherein said catalyst layer has a thickness of between approximately 1 nm and approximately 2 nm.
 36. The method of claim 34 wherein said substrate is a silicon substrate.
 37. A method of growing carbon nanotubes on a substrate having a catalyst coating, the method comprising: growing said carbon nanotubes on said substrate by chemical vapor deposition; removing said carbon nanotubes from said substrate; and growing additional carbon nanotubes on said substrate without removing said catalyst coating from said substrate.
 38. A method of forming a plurality of carbon nanotubes using a floating catalyst comprising: flowing a gas comprising a group VIII element into a reactor; flowing a gas comprising a non-catalytic element into said reactor; wherein said group VIII element and said non-catalytic element react to form said floating catalyst; and flowing a plurality of reactant gases into said reactor to form said carbon nanotubes.
 39. The method of claim 38 wherein said non-catalytic element is a lanthanide and said floating catalyst comprises approximately 5 to approximately 95% by mass of said lanthanide.
 40. A method of forming a plurality of carbon nanotubes on a substrate comprising: depositing a composite catalyst layer on a first side and a second side of said substrate, wherein said composite catalyst layer comprises a group VIII element and a non-catalytic element, said non-catalytic element comprising a metal that does not catalyze nanotube growth by itself; oxidizing said composite catalyst layer to form an oxidized composite catalyst layer; reducing said oxidized composite catalyst layer to form a reduced composite catalyst layer; positioning said substrate to grow said carbon nanotubes on said reduced composite catalyst layer on said first side and said second side of said substrate; and growing said carbon nanotubes on said first side and said second side of said substrate simultaneously. 